Near-Band Gap Selective Photoluminescence in Wurtzite GaN

Abstract

Selective photoluminescence (SPL) experiments are performed at low temperature on n-type GaN layers obtained by epitaxial lateral overgrowth on sapphire. A significant impurity electronic Raman scattering (ERS) effect is observed when excited in the spectral range of excited states of A and B free excitons, giving an accurate determination of the transition energies to the n = 2 states and a straightforward estimation of the A and B Rydberg. From the donor transition energy measured on the ERS spectra we deduce a 30.5 meV binding energy for the main residual donor in our epitaxial layers. In addition, SPL experiments have been used to analyse the neutral donor bound exciton (I2) spectra. It is shown that a laser tuned near the A free exciton induces strong and narrow resonant peaks superimposed to I2. It is concluded that such effect is due to the selective excitation of inhomogeneously broadened I2 excited states. Up to five rotational I2 excited states are identified.